Coded track circuit system of railway signaling



' April 14, 1942. R. ALLISON CODED TRACK CIRCUIT SYSTEM OF RAILWA? SIGNALING Filed April 5, 1941 2 Sheets-Sheet 1 swmmm INVENTOR Les Allison H15 ATTORNEY April 14, 1942.

I L. R. ALLISON I 2,280,620

.G ODED TRACK CIRCUIT SYSTEM OF RAILWAY SIGNALING Filed April 3, 1941 2 Sheets- Sheet 2 I mv NT OR Le la? [lemon H15 ATTORNEY plied to a coded feed 'bination which is organized. as in the earlier re:

Patented Apr. 14, 1942 comic TRACK omoUI'rsYs'rEM or AIL- WAY SIGNALING Leslie R. Allison, Forest Hills,-Pa., assignor to The Union Switch & Sign Pa., a corporation of Pennsylvania.

a1 Company,

Swissvale,

Application April 3, 1941, Serial 386,615 8 Claims. (01. 246-33) My invention relates to coded track circuit systems of railway signaling and ithas special reference to A. P. B. and othertwo-direction running systems of this character wherein'use is made of the coded feed backfoperating principle that first was disclosed by Frank H. Nicholson Patent No. 2,021,944 (issued November 26, 1935) and that also is shown by numerous later patents and applications of common ownership herewith.

Generally stated the object of my invention is to overcome a reset difficulty which is experienced with coded feed back tions when they are included in" A. P. B. systems of the combined master-feed back-special code track circuit combinaenergy type which the following copending. ap-

plications disclose and claim: Serial No.294,89'7, filed September 14, 1939, by Ralph R. Kemrnerer; Serial No. 382,431, filed March8, 1941, by Frank H. Nicholson; and Serial No. 386,642, filed April 3, .1941, by Ralph R. Kemmerer and Crawford E.

Staples. i I l A more specific object is to increase the effectiveness of track circuit reset facilities of the code period interchange Gilson application Serial No. 3, 1941) discloses and claims. r

Another object is to utilize the Gilson principle of code period interchange for preventing A. P. B. systems of the special code type above named from cascading a reset operation requirement back and-forth from one end of the A. P. 13. stretch to'theother.

In practicing my invention I attain the above and other objects and advantages by: (1) supplementing the. codesupply apparatus at one end of each track section in the A. P. B. stretch by an auxiliary device which when operated interchanges the on and off periodsof the coded energy which is supplied to the section rails at the device location; that this device will delayedly operate in response to each restoration of the adjoining track section to its normal coded feed back form of vacant section operation. 1

I shall describe an A. P. 3. system track circuit organization which embodies my invention, and shall then point out the novel features thereof in claims. This illustrative embodiment is disclosed in the accompanying drawings in which:

type which Robert M.

386,642 (filed April erred. to Nicholson application {Serial- No. 382,431; I 1

. Fig. 2 illustrates the various'forms of coded energy which are effective in the track circuit combination of Fig. 1 before, during and after my new apparatus functions to effect a reset of the combination; and

. Fig 3 is a fragmentary showing of the reset apparatus. of Fig. 1 modified to make use of a code period shifting device which is energized over a back instead of a front contact of the relay that responds torestoration of the adjacent track section to the normal .coded feed back form of vacant section operation. v

In the several views of the drawings like reference characters designatecorresponding parts. Referring first to Fig. 1, I have there reproduced, in a form modified as the track circuit combinations of the A. P. 13. system which Nicholson application Serial No. 382,431 discloses and claimsr i 7 Track circuit combinationofjFi g. 1 The track section to which the Nicholson structure of Fig. 1 is appliedforms part of the usual siding-to-siding A. P. B. stretch (not comj pletely shown in Fig. 1 hereof) of two-direction and (2) arranging Fig. 1 is a diagrammatic showing'of theanticascade reset improvements of my invention apback track circuit comrunning track of that stretch which locations II and III.

with the usual wayside signals SEII and SWIII by which the entry of eastbound and of west- ,governed. These two signals, 1 trolled through on the fcoded feed back 1 mentionedNicholson 4O ,tem' of the non-line-wire character which the earlier identified Nicholson applicationdisclosfes and claims, these two reversely arranged track circuits cooperate with corresponding facilities l-- and it includes the portion is between intermediate This section is equipped bound. traffic into the section is respectively in turn, are conthe medium of two coded track circuits which are reversely arranged and which operate (under vacant track stretch conditions) principle of the earlier Patent No. 2,021,944.

When organized into a complete A. P. B. sysof adjoining track sections (not completely illustrated herein) in a manner enabling each train that enters the A. P. B. stretch to establish both directional and following protection without the aid of line wires for signal control purposes.

; The non-line-wire A. the track circuit combination of Fig. 1 has been reproduced is broadly similar to that of-the Nicholson application and differs therefrom only by minor changes in system arrangement and individual element design. These differences to certain details, one of P. B. system from which circuits in the usual manner.

at the 180 rate;

. rails |2 with are of detail rather than of principle and will, it is thought, become evident from the following description of the Fig. 1 track section II III and the apparatus directly associated therewith.

In this track circuit organization of Fig. 1, the master energy source B-XCX is at the section west end II and it transmits on period pulses of master code energy to a master track relay TR' at the section east end; the source BKCK is v transmits off period pulses of feed back energy to a feed back track relay TRA at the section west end; the westbound wayside signal SWIII is controlled by the master track relay 'ITR, through the medium of home and distant decoding relays HW and DW; and the eastbound wayside signal SEII is controlled by the feed back track relay TRA through the medium of corresponding decoding relays HE and DE.

Each. set of these decoding relays HWDW and HEDE is supplied with pick-up energy .over apole changing contact 1 of the associated track relay and the two relays of the set have the usual frequency code form of response characteristics. That is, both relays in each set stay released when the controlling track relay .(TR or TRA) fails to follow code; the home relay '(HW or HE) picks up whenever the controlling track relay follows code of either a '75 or a .180 pulse per minute frequency; and the dist'ant'i relay (DW or HW) picks up only when feed back energy .the controlling track relay follows code of the 180 pulse per minute frequency.

This selective response by the distant relays DWand DE is produced by frequency selective units I8DDU interposed in the relay energizing The necessary rectification of the current which the decoding transformers DTW and DTE supply to the 'home relays HW and HE is effected by track relay contacts 4 arranged as disclosed and claimed by a copending application Serial No. 210,744, filed May 28, 1938, by Frank H. Nicholson et al., now D. S. Letters Patent 2,237,788, granted April 8; 1941.

.The indication which westbound signal SWIII displays is determined by east-end decoding resignal SEII is similarly controlled by west-end decoding relays HE-DE. In each instance the controlled signal shows: (1) clear when the associated track relay (TR. or 'I'RA) follows code (2) approach when the track relay follows code at the 75 rate; and (3) stop when the track relay fails to follow code.

Coding of the master energy that is supplied to the section at west location II is efiected by When picked up these contacts connect (through transformer TTW) the section source BXCX and thereby produce a master code on period; when released these contacts transfer the rail connection to track" relay TRA and thereby produce a master code oif? period.

.Serving to drive this repeater relay CP are a pair of code transmitters IBOCT and 150T installed at location II and rovided with contacts I80 and '15 which pick up and release at the respective frequencies of 180 and '75 times per which of these contacts is included in the repeater relay driving circuit is made by a contact N2 of the westbound decoding relay HW for at that east end III and it the next track section to up) relay GP to produce a consisting of 75 on master energy code period ulses per minute.

westbound train moves through the A. P. B. stretch.

For contributing to a corresponding control of the eastbound wayside signals SE use is made of feed back track circuit apparatus earlier referred to as supplementing the master organization just described. As already stated, this apparatus includes the track relay TRA at the section West end II and the trackway source BKCK at the section east end III. During the off periods of the east-end received master code energy, the before mentioned impulse relay RC connects this source with the section rails over the front points of its contacts INS-Ill and thereby supplies the rails with the pulsed feed back energy by which the west end track relay TRA is operated.

Both in function and in operation this impulse relay RC closely resembles a supplied to the relay these contacts pick up and transfer the rail connection to the feed back source BKCK.

and transmitted to relay RC through a trans- The primary of this transformer is connected with winding I20 over either a front contact I22 of the eastbound decoding relay HE for the next section to the east or the back point of contact I22 in series induce in Winding polarity potential. mary and secondary circuits for transformer I2I I I1 thereof Such. pick-up,

WS atlocation II; and

' or another of. the code -modulated energy the term Relay RC responds only to positivefpolarity relay TR causes decoding transformer DTW to I20 a pulse of such positive When the just described priare both complete, each of those. positive pulses is transmitted. to relay RC and produces a momentary pick-up on the part of contacts ,I I6- as. already pointed out, connects the section rails with east end source BK-CK and causes a short pulse of feed back energy to be supplied thereto.

Under theconditions just described, each of these pulses coincides with, an off period of the west end supplied master code and hence is transmitted over the section rails to west location II and: there impressed upon the feed back track relay TRA through transformer 'ITW, back contacts IIll-I II of device CP and a rectifier I30. This west end track relay TRA is, in consequence, caused to pick up its contacts 1-4 in step with the "ofi period pick-ups of the east end impulse relay RC. 9 By the associated decoding relays HE-DE that response is, in turn, translated into appropriate indication selections for the eastbound signal SEII, I I s For the purpose of equalizing. the pick-up and release times of the so operated feed back track relay TRA, its pick-up circuit is supplemented by a stick circuit which prolongs each of the relay pick-ups for the full duration of the off period during which the pick-up occurs This ,stick circuit includes a back contact I33 of the master coder relayCP and a frontcontact I34 of the track relay; it is supplied with energy over either a front contact I35 of the westbound decoding relay I-IW for the next section to the west or theback point of contact I35 and a front contact I36 of the westbound directional stick relay itoperates in the same manner as that disclosed and claimed by Patent No. 2,172,893 which issued to Edward U. Thomas on September 12, 1939.

Under other conditions (which will be made more evident presently) the east end relay RC operates not asan impulse device for the supply of feed back pulses during the master code same location.

ofi periods but instead as a repeater for one transmitters IBIICT and 150T at location III. .Under these other conditions the energy supplied from source BK- -CK over front. contacts pendently of the location II. To

I I6 -I I1 is modulated indemaster code pulses from west designate this independently special code will be employed. s s I During these just referred to other conditions,

, a driving circuit for relayRC is set upjover back contacts I26 and I25of relay WS and HW; This driving circuit has much in common with certain correspondingfcontrol pathsthat an application Serial. No. 315,801 filed by Crawford E. Staples on January26, 2,244,901, granted June 10, 1941, discloses for headblock location devices KR. It includes a selector contact I38 of the eastbound decoding relay HE for the track section to the east of location III. When picked up this contact assigns the driving circuit to the back point of the code transmitter contact I80 at, the samelocation; when released it transfers thecircuit connection to the back point of the code transmitter con- 1940,. now U. S. Patent shows and describes.

would set the signal interfere with the desired tact 15 over a path thatincludes a front contact I39 of the eastbound stick relay ES.

Comparing the sets of code transmittersCT which are shown at the two locations 11 and III it will be noted that at each location the back point connections which the preceding paragraph The above mentioned relays ES and WS are directional stick devices of the character ordinarily used in two direction running. systems of A. P, B. signal control. One set of these relays ES-WS is provided at each of the two ends 11 and III of the Fig. 1 track circuit and control thereof may be over local energizing circuits (nothere shown) equivalent to those which the earlier named Kemmerer application Serial No.294,89'7

When arranged in that customary A. P. B. manner both ofthe relays in each ES-WS set will be deenergized and stay released (as shown in Fig. 1 of thepresent application) as long as the A. P. Bnstretch of single track remains vacant. Upon movement of a westbound train through the stretch the normally. released westbound relay WS at a given intermediate location will pick up when the leading vehicle bound train first passes that location and so stay until the trailing vehicle of the train clears the west end of the section of which the given location marks the east end. Similarly, upon move,- ment of an eastbound train through the stretch, the normally released eastbound relay ES at a given intermediate location will be picked up only leading vehicle of the be seen that the oil periods of the west end sup-' plied master code recur at the frequency rate; that the feed back relay TRA at location 11 is by off period energy received from the section east endcaused to follow code at the same rate; and that the associated relays HE--DE ordinarily SEII at clear. For a purpose which need not here be considered, however, the pick-up circuit for distant relay DE is broken, under these conditions, by a contact I3I of the westbound decoding relay HW at location Signal SEII is, in consequence, normally held at approach. This holding, however, does not clear showing upon the approach of aneastbound train. Upon such approach the west bound decoding relay I-IW (at location II) for the next section to the west releases and restores (at contact I3I) the control of eastbound decoding relay DE to track relay TRA. The westbound stick relay WS at location 11 also is released and in consequence the master coderrelay CP at the same location is maintained (at contacts II2-I I4) continuously deenergized. This deenergization .keeps (at I back contacts IIlJ-III) the west end track relay TRAcontinuously connected with the rails of section II-III, removes all master code energy therefrom, .eIIects the release of westbound decoding of the west-c it thus provides the desired contact I to assign'the control of impulse relay RC to one or the other of the eastend code transmitters |80CT and I5CT. Under vacant conditions of the track section to the east, relay HE at location III will be picked I38 thereof now will assign the impulse relay driving circuit to the back point of transmitter contact I 80.

This assignment causes relay RC 'recurrently to pick up at the frequency of 180 times per minute and thus supplies section IIIII with special code energy (from east end source BKCK) in the form of pulses that recur at the frequency of 180. per minute. In being received at the west location II these special code pulses operate track relay TRA and both of the decoding relays HE-DE. quence the eastbound wayside signal SEII now shows clear.

Should the track section to the east of location III be occupied by an advance east bound train the indication displayed by signal SEII will be approach instead of clear. This comes about as follows. The follom'ng train in the section to the West of location II still acts through relays H WS and HW at that location to keep (at contacts ,l|.2ll4) the master coder relay CP continuthe east of location III keeps relay HE thereat released and causes the eastbound stick relay ES at the same location to stay picked up. Contact l38of relay HE now assigns (over front contact 139 of relay ES) the impulserelay driving circuit to the back point of code transmitter contact 75. This assignment causes relay RC recurrently to pick up at the frequency of 75-times per minute and thus supplies the section rails with special code energy (from east end source BKCK) of the 7.5 pulses per minute variety. In being received at location II this special '75 code energy operates track relay TRA and thereby causes eastbound signal SEII to show approach, as aforesaid.

Should, finally, the advance train be in sectionII-III, the eastbound signal SEII will display stop. This, of course, results from the usual deenergization of track relay TRA and the consequent release of both of the eastbound decoding relays HEDE at location II.

The combined feed back and special code track circuit organization which has just been described in connection with Fig. 1 is, therefore, effective to control the eastbound signals SE in the usual automatic block system manner and when expanded into a complete A. P. B. system following protection for all eastbound train moves through the A. P. B. stretch.

Such a complete A. P. B. system will, quite obviously, also olIer .all of the usual features of directional protection signal control. Since these do not form a, part of the present invention, detailed description thereof will not here be given. It may, instead, be said that: (1) in the provision of westbound directional protection use is made of knockdown contacts I23 carried by the eastbound stick relays ES and arranged to prevent the westwardly extending sections from receiving feed back-energy (from source BK-CK) up and contact.

plied) pulses of special during passage of westbound trafiic through the stretch; and (2) in the provision of eastbound directional protection use is made of other knockdown contacts H4 carried by the westbound stick relays WS and arranged to prevent the eastwardly extending sections from receiving master 75 code energy (from source BX-CX) during the passage of eastbound traffic through the stretch.

The reset problems of Fig. 1

of each A. P. B. system track circuit under certhe two ends of the circulted section are supplied with master and special code energy pulses which coincide with and hence directly oppose each other.

In the case of the track section which Fig. 1 shows at IIIII, such conditions exist when the West end supplied (from source BX-CX) pulses of master code energy recur at the same frequency as and directly coincide with the opposing pulses of east end BKCK) special code energy. Under those conditions the west end supplied pulses of master energy may have the character shown at master 180 (original) in Fig. 2 and the east end supplied pulses of special energy may have the directly coinciding character which is shown at special 180 in Fig. 2.

It is true that the west end and the east end coding devices CTI by which these master also frequently happens that contacts I80 of device CT at location III may get and stay in exact synchronism with contacts of device CT at location II.

To overcome the condition just stated, the

Gilson application supplements the code supply apparatus at one end code energy pulses independently supcode energy and thereby permits the master energy pulses to reach the master track relay at the feed back section end.

and the opposing (and still other certain reset requiring impulse relay RC to contact In responding in the usual manner thatrelay nowdiscontinues the special. code energy, substitutes off period pulses of feed back energy therefor and thereby restores the track circuit to the desired coded feed back? form of vacant section operation. -I

My present invention concerns itself with the effect on a particular section of actions which take place in one of the adjoining sections of the A. P. B. stretch. This efiect is to be distinguished from the problemsof initial reset with which the Gilson application deals and it results in what will be termed a cascading of the reset operation requirement from one section to another. r The resulting problem of reset cascading results from the fact that A. P. B. systems which include track circuits of the Fig. 1 (hereof) type are found to transfer from. one section to anconditions. Laboratory tests, moreover, demonstrate that this cycling of thereset operation requirement may incertain cases becascaded back and forth from one end of the A. P. B. stretch to the other several times before permanent reset is effected. In the A. P. B. system which the diagram of Fig. 1 partially represents, this phenomena of i reset operation cascading may be produced in the following manner. If, with the entire A. P. B. stretch initially vacant, the rails of the section to the immediate west of location II are subjected ma shunt the westbound code detector relay I-IW (at location 11) for that west section releases; That release opens (at contacts H2 and H4 of devices HW and WS) the driving circuit for master coder relay CP at location IIand thereby removes all master code energy from the rails of section II-- i I At thejeast location III, in consequence, master track relay TR becomes continuously deenergized and releases device HW. That release assigns (at contact I25) the driving circuit for I811 of east end code transmitter IBOCT and thus causes the rails of section II-III to be supplied with special code energy of the 18.0 pulse per minute variety.

, When, now, the shunt is removedyfrom the section to the west of location II and the track circuit for that section initially resets (as by aid of a code converter relay of Gilsons CCR typenot here shown) the resulting pickup of relay I-IW at location II restores the control of the master coder relay GP to west end. transmitter I80CT. In consequence the rails of section II-I II now once more are supplied with master code energy of the 180 pulse per minute variety. Quite obviously, now, section II--III must go through the before explained operations of reset before the normal coded feed back form of vacant section operation can be restored thereto.

At the east location III, meanwhile, the re lease of relay HW which accompanies the requirement for reset by section II-III affects the track section to the driving circuit of relay CP (not shown) therefor and thereby removing all master energy from r the rails of that east section. Upon reset of section II-III and the resulting pick-up of relay HW at location III, in consequence, the just de-- scribed reset requiring conditions are transferred to the track section to eastof location III. In the manner just set forth, accordingly,the requirement for track circuit reset may be prothe immediate east by breaking 6 1 gressively transferred from section to section in the direction of from west to east.

Under certain further conditions, moreover, similar progressive transfer or resetrequirement also may take place in the opposite or east-to west direction. One manner in which this might come about will now be described.

Upon removal of a shunt therefrom, section 11-111 of Fig. 1 may initially'reset in one of the manners earlier explained; the resulting pick-up of relay HE at location II then effectsan im-, mediate reset of the section to the west of that locationand thereby causes succeeding sections to the west similarly to reset; and the accompanying pick-up of relay HW at location III then assigns the control of the there located coder relay RC to transmitter l8llCT.

If in the section to the immediate east of location III a now occurs, reset of the track circuit for that section will be delayed. Because of this delay relay HE at location III now drops and by deenergizing (at contact I22) relay RC at the same location removes BK-CK energy from the rails of II-III and thereby effects the release of relay HE at location II. Section II-III now has, in consequence, lost its initial reset.

The reset loss. action just described may,

moreover, repeat itself into successive track sections to the west of location II. As a result, quite obviously, therequirement for track circuit reset 0 also may be progressively transferred from section to section in the direction of from east to west.

Under the above stated and certain other conditions not; herein described, a requirement for track circuit reset thus may cascade itself. in either direction throughout the entire length of the A. P. B. stretch. The earlier mentioned laboratory tests confirmthat such cascading is more than. a mere possibility; it, in reality, constitutes a serious obstacle to the successful operation of coded A. P. B. systems of the type herein considered.

The reset apparatus oj Fig. 1

To overcome the cascading difficulty just stated, I propose to use apparatus which may supplement either the special code pulse supply equipment atthe feed back end of each section or the master code energy supply equipment at the master section end. At either location this apparatus takes the form of an auxiliary relay which upon restoration of the adjacent track circuit to its normal coded feed back vacant section operation delayedly interchanges the on and theofi" periods of the there supplied code and thus disrupts any reset preventing coincidence of the master and special code energy pulses.

.That disrupting action effectively assures that themaster code energy will reach the trackrelay TR. at the feed back end of the section. By responding in the usual manner, that relay now discontinues the special code energy, substitutes off period pulses of feed back energy therefor and thereby restores the section to its normal coded feedback form of vacant section operation. This restoration is progressively duplicated by successive adjoining sections wherein the requirements for reset may have been set up.

In the embodiment of my invention which is shown for section II--III of Fig. 1, this auxiliary relay takes the form of a device FL installed as cascading of the clashing of opposing code pulses gized over a front contact IOI of the westbound code detecting relay HW for the next track sec- Under picked up conditions of relay FL, this contact Illfl'connects (as shown) the CP driving circuit with the front point of contact I80 of the code transmitter I80CT at location II; when, however, relay FL is released, contact I transfers the named connection to the back point of a companion contact I80a of the same trans- Each shift, therefore, in the position of contact I00 causes the coder relay CF to interchange the"on and the off periods of the master code energy which is supplied to the west end" of section IIIII.

Current for energizing this relay FL is supplied" to the winding thereof over the frontpoint of a contact I0'I which is carried by the westbound decoding relay HW for the'next section to the west of location II. As long, accordingly, as" that west section relay I-IW is picked up, relay FL holds contact I00also picked up; when, however, the controlling relay HW releases, contact I'0I breaks the energizing circuit for relay FL and allows contact I00 also to release. For a purpose to become more evident presently, this contact I00 of relay FL is given a short period of'pick-up delay.

In examining how the reset facilities of Fig. I operate, let it be assumed that the track circuit combination of that figure is included in a multi-section stretch of A. P; 13. track and that each section in that stretch is equipped with apparatus which duplicates the equipment of Fig. 1;

Undervaca-nt conditions of that entire stretch all of the-track circuit combinations therein are operatinginthe normal coded feed back man ner; the eastbound and the westbound decoding relays HE and HW for each of the circuited sections are picked up; and the pulse-shifting relay FL for each section thus also is picked up:

Assume now that an eastbound train comes into-the section which is to the immediate west of'location II. At that location this train efiects the release of relay HW and thereby causes: (1') relay FL to release contact I00; and (2) relay CP to be disconnected (at contacts II2I I4) fromboth of the code transmitters I80CT 750T; That relay CP now discontinues the supply of master code energy to the west end II of section II-III and thus continuously releases the track relay TR at the section east end III.

The resulting release of relay HW at location III assigns (at contact I25) the control of impulse relay RC to code transmitter I 800T at the same location and thereby causes the rails of section IIIII to be supplied with special code energy of the 180 pulse per minute character. Thisenergy flows westwardly and operates track relay TRA at location II.

Assume next that the eastbound train leaves the section to the west of location II by way of an intermediate spur siding (not shown). lowing this removal of section rail shunt, the track section-for-that west section initially resets (as by aid-ofa code converter relay of Gilsons before mentioned CCR typenot here shown) and the resulting pick-up of relay HW at locau of themaster code up the interfitting of transmitter contact tion II: (1) completes (at contact IN) the. ener- FL; and (2.) connects (at contact H2) the driving circuit for relayCP with code transmitter I 800T. That connection This energy tries to flow' eastwardly to track back form of vacant section operation. 20

' Meanwhile, relay FL at location II picks up (at the end of its period of response delay) and transfers (at contact I00) the driving connection for master coder relay CP from the back point of transmitter contact [80a to the front point I80; already having reset, however, the resulting interchange of master code on and off periods does not disturb the coded feed back vacant section operation.

In the event, however, that the pulses of westend-supplied master 180 code initially do coincide (see the upper portion of Fig. 2) with the pulses. of east-end-supplied"special180 code, then both. of the track relays TR and TRA are deprived: of

relation of' opposing energy pulses which the lower portion of Fig. 2 represents.

now does I receive operating energy fromthe section rails,

tion III, that pick-up transfers (at'contact I25) the driving circuit for impulse relay RC from code transmitter: IBOCT to winding I20'of decodfoundit'o' be satisfactory for relay FL.

Use of reset apparatus of the just described Fig; l'type is'found to safeguard adjoining track sections ina. vacant A. P. B. stretch from having their cod'ed' feedback form of operation objectionably' interfered with and thus it effectively prevents any original reset requirement from be- The track circuit form of circuit of master ing cascaded backand forth through the A. RB." stretch before permanent reset is effected. p The reset facilities of Fig. 3

. In Fig. 3 I have shown. resetrfacilities which difier from those of. Fig. 1 only through a substitution forslow pick-up relay FL of a slow release pulse-shifting relay BL. This relay BL is energized over the back point of contact. lfllof the westbound decoding relay HW for the nexttrack section to the .west. The contact I00 thereofis included inthe driving circuit (contact H2 and conductorcfi) [for the master coder relay CP (not shown inFig. 3) at :the relay location. This contact 100 has a period of release delay which is. of the: samemagnitude as is the pick-up delay periodfor contact Hill of the earlier described relayFLofFig. 1. i J

In .explaining how the reset facilities of Fig. 3 operate, assume that the complete track circuit combination of Fig. 1 has relay FL thereof replaced. by device .BL' of Fig; 3. Under vacant conditionstof the AUP. B. stretch of'which track section .II-i-III formsa part, relay HW at location II is picked uptcode-shiiting relay BL is released, and contact I00 connects the master coder (device CP) drivingcircuit. with the of the code transmitter contact l8lla.

.As, now, an eastbound train enters HW at that location releases and thereby: (1) picks upf(over. contact lflllrelay BL; and (2) disconnects"(attcontacts Il2-fl M) ;the driving coder relay CP from both of the code transmitters l80CT--15CT. x K

it Should this eastbound train now move out of thesection to the west of location II by way of an intermediatepasslng siding, there will result in section III-+111 a series of actions which are identical with those earlier described for Fig. .1 Withbut asingle exception. This exception is that the initial pick-up of decoding relay HW at location II isresponded to by a delayed release of contact Hill of relay BL instead of a delayed pickupof contact; I 00 of relay FL. 1 That delayed release assures. prompt reset of the track section in exactly the same manner as has already been explained for the reset facilities of .Fig. 1.: Because of thisidentity, further detailed description of .how the Fig. 31 apparatus operates is not believed to be necessary. i

' Summary ..;Although the reset cascade prevention facilities of. my invention are as being used with coded feed back track circuit combinations of onlyone A. P. B. system form (Fig. 1),1it will beobvious that such use is illustrative rather than restrictive and that my new cascade prevention facilities will also have utility with, and hence may be applied to signaling system controlcircuit combinations ofv still further formswherein. a condition of opposing codepulse coincidence may at times be transferred from one circuit combination to another. :Fron'i the foregoing, accordingly, it will be seen that I have made important contributions to coded track circuit systems of naling. In particular I have overcome a reset which is experienced with coded feed bac track circuit combinations when they are included in A. P.1B. systems of the combined master-feed back-special code type hereinbefore describedgl. have increased the efiectiveness of. track circuit reset facilities of the code period herein shown and described back point thetrack section to theimmediate west of location 11, relay eration only when said 1 maintained inactive by code energy in. the form of recurring pulses that section driven by the two-direction sigi with the i off the spirit and scope of my invention.

interchange type which Robert M. Gilson application Serial No. 386,642 discloses and claims; and I have utilizedithe Gilson principle of code period interchange for preventing A. P. B. systems of the coded feed back track circuit type from cascading a reset requirement back and forth from one endof the A. P. B. stretch to the other. i i

Although'I have herein shown and described only two forms (Figs. 1 and 3) which apparatus embodying my invention may take, it is under stood that various changes and modifications may be made in that apparatuswithin the scope of. the. appended claims without departing from Having thus described my invention, what I claim is:

1.; In combination, a stretch of two-direction running railway track, adjoining track sections included in said stretch, master code equipment located at the junction of said first and second sections and effective to supply the second section rails with master code energy in the form of recurring on period pulses that are separated by ofi period intervals, feed back apparatus located at the remote end of said second section and operable when and only when said master code pulses are there received further to supply the second section rails with feed 1 back energy in the form .of pulses that recur in step with the off periods of the received master code, supplemental equipment also at the remote end of said second section which comes into opfeed back equipment is failure of said master energy to reach the equipment location and which then supplies the second section rails with special have no regular time coincidence with the aforesaid master code off periods, means for maintaining, said second section master code equip,.

ment inactive under shunted conditions rails of said first section, and means effective uponremoval of a shunt from said first section ,rails for delayedly interchanging the.

fon. and the 0 periods of said second section master code whereby to disrupt any vacant section coin- "cidence of said special code and master energy pulses that may have prevented those master pulses from earlier reaching said second section remote end and there restoring said feed back apparatus to its normal condition of vacant section. operation.

2. In combination, .a stretch of two-direction running railway track, adjoining first and second track sections included in said stretch, master equipment at the junction of said two sections operated by a master coding contact over a driv ing connection therewith and effective to supply the rails of said second section with master code energy in the form of recurring on period pulses that are separated by off backapparatus at the remote endof said second there received pulses of said mastercode energyand operable duringand only during said master'pulse reception further to supply the second section rails with feed back energy in the form of pulses that recur in step periods ,of the received master code, supplemental equipment. also at said second section remote end operated by an independent coding contact over a driving connection herewith and effective onlywhensaid feed back apparatus is maintained inactive by failure of said master energy to. reach the equipment loca'-' first and second i of the.

period intervals, feed tion still further to supply the second section rails with special code energy in the form of recuring pulses that have no regular time coincidence with the aforesaid master code ofi periods, means for maintaining said second section master code equipment inactive under shunted conditions of the rails of said first section, and means effective upon removal of a shunt from said first section rails for delayedly interchanging the on and the off periods of said second section master code whereby to disrupt any vacant section coincidence of said special code and master energy pulses that may have prevented those master pulses from earlier reaching said second section remote end and there restoring said feed back apparatus to its normal condition of vacant section operation.

3. In combination, a stretch of two-direction running railway track, atrack section included in said stretch, master equipmentv at a given end of said section operated by amaster coding device over a driving connection therewith and effective to supply the section rails with master code energy in the form of recurring on period pulses that are separated by 01f period intervals, feed back apparatus at the opposite end of said section. drivenv by the there received pulses of said master code energy and operable during and only during said master pulse reception further to supply the section rails with feed back energy in the form of pulses that recur in step with the off periods of the received master code, supplemental equipment also at said opposite section end operated by an independent coding device over a effective only whensaid feed back apparatus is maintained inactive by failure of said master energy to reach the equipment location still further to supply the section rails with special code energy in the form of recurring pulses that have no regular time coincidence with the aforesaid master code off periods, a relay at one of said two section ends which delayedly responds to predetermined changes in the traflic conditions of said stretch, and means rendered effective by each of said relay responses for shifting the said equipment driving connection at the relay location from a first to an opposed contact point of the associated coding device whereby to interchange the on and the off periods of the said coded energy that said device driven equipment supplies and thereby disrupt any vacant section coincidence of said special code and master energy pulses that may have prevented those master pulses from earlier reaching said opposite section end and there restoring said feed back apparatus to its normal condition of vacant section operation.

4. In combination, a stretch of two-direction running railway track, a track section included in said stretch, master equipment ata given end of said section operated by a master coding device over a driving connection therewith and effective to supply the section rails with master code energy in the form of recurring on period pulses that are separated by off period intervals, feed back apparatus at the opposite end of said section driven by the there received pulses of said master code energy and operable during and only during said master pulse reception further to supply the section rails with feed back energy in the form of pulses that recur in step with the oil periods of the received master code, supplemental equipment also at said opposite sectionend driving connection therewith and which is operable only when saidfeed back apparatus is maintained inactive by failure of said master energy to reach the equipment location and which then supplies the section rails with special code energy in the form of recurring pulses that have no regular time coincidence with the aforesaid master code off periods, a relay at said given section end which delayedly responds to predetermined changes in tion end and there restoring said feed back apparatus to its normal condition of vacant section operation.

5. In combination, a stretch of two-direction running railway track, a track section included in said stretch, master equipment at a given end of said section operated by a master coding device over a driving connection therewith and effective to supply the section rails with master code energy in the form of recurring on period pulses that are separated by 01f period intervals, feed back of pulses that recur in step with the ofi periods of the received master code, supplemental equipwith master code energy in the form of recurring on period pulses that are separated by ofi period intervals, feed back apparatus at the opposite end of said section driven by the there received pulses of said master code energy and operable during and only during said master track section included iary relay at one of said is picked up during certain trafiic conditions in i said stretch and which releases a short time fol- Uand only during said ceived master code, supplemental equipment also at said opposite section end operated by an independent coding contact over a driving connec-- tion therewith and effective only when said feed back apparatus is maintained inactive by failure of said master energy to reach the equipment location still further to supply the section rails with special code, energy in the form of recurring the aforesaid master code off periods, an auxiltwo section ends which lowing a predetermined change in those conditions, and means rendered effective by each of said relay releases for shifting the said master equipment drivingconnection at the relay location from a first to an opposed contact point of i said master coding device whereby to interchange the on and the "off periods of the said master 7 for shifting the said driving pulses that have no regular time coincidence with r ment location and which thensupplies the section rails with special code energy in the form of recurring pulses that haveno regular time coincidence with the aforesaid master code off periods, a relay at said given section end which delayedly responds to predetermined changes in the traffic conditions of said stretch, and means rendered effective by each of said relay responses connection for said master equipment from said back master coding contacts to said front master coding contact whereby to interchange said master codeon and off periods and thereby assure restoration of said feed back apparatus to its normal condition of vacant section operation.

8. In combination, a stretch of railway track,

. a track section included in said stretch, master code energy that said driven equipment supplies" and thereby disrupt any vacant sectionvcoinci dence of said special code and master energy pulses that may have prevented those master energy pulses from earlier reaching said opposite section end and there restoring said feed back apparatus to its normal condition of vacant section operation.

i 7. In combination, a stretch of railway track,

a track section included in said stretch; master equipment at a given end. of said section operated by either a front or a back master coding con tact over a driving connection fective to supply the section railsfwith master code energy in the form of recurringfon period pulses that are separated by off period inter vals, feed back apparatus at the opposite end of said section driven by the there receiving pulses of said master code energy and operable during master pulse reception further to supply the section rails with feed back energy in the form of pulses that recur instep with the off periodsof the received master code, supplemental equipment also at said opposite section end which is operable only when said feed back apparatus is maintained inactive by failur of saidrmaster energy to reach the equip equipment at a given end of said section operated by either a front or a back master coding contact over a driving connection therewith and effective to supply the section rails with master code energy in the form of recurring on period pulses that are separated by off period intervals, feed back apparatus at the opposite end of said section driven by the there received pulses of said master code energy and operable during and only during said master pulse reception further to supply the section rails with feed back energy in the form of pulses that recur in step with the off periods of the received master code, supplemental equipment also at said opposite section end which is operable only when said therewith and effeed back apparatus is maintained inactive by failure of said master energy to reach the equipment location and which then supplies the section rails with special code energy in the form of recurring pulses thathave no regular time coincidence with the aforesaid master code off periods, a relay at said given section end which delayedly responds to predetermined changes in the traff c conditions of said stretch, and means rendered effective by each of said relay responses for shifting the said driving connection for said master equipment from said front master coding contact to said back 'master coding contact whereby to interchange said master code on and foff periodsand thereby assure restoration of said feed back apparatus to its normal condition of vacant section operation.

a V LESLIE a, LISON, 

